The present invention relates to a fluid flow operated power generating system for generating electrical power. The invention also relates to a method of constructing a fluid flow operated power generating system and to the use of a fluid flow operated power generating system.

Electricity can be generated by using hydropower, i.e. the production of electrical power through use of a fluid (in most cases water) flowing along an electrical power generator. Most hydroelectric power comes from the potential energy of dammed water driving a water turbine and generator. Instead of potential energy one can also take advantage of the kinetic energy present in a water flow. For instance, in a run-of-the-river hydroelectric power station use is made of the natural flow of a river. Power stations of this type may be built in rivers with a consistent and steady flow, either natural or through the use of a large reservoir at the head of the river which then can provide a regulated steady flow for stations down the river. In another type of power station use is made of tidal energy. In this type of station the kinetic energy of water masses moving under the influence of the earth-moon gravity is used in order to power the generator(s). Tidal power generators have a particular low ecological impact and potentially are able to provide large amounts of energy.

In general the velocity of the water flow caused by the tidal forces produced, is relatively low, typically not more than several m/s. In order to operate the generator of a power station the velocity of the water should be as high as possible, so that conventionally tidal power stations are arrayed in high-velocity areas where natural tidal current flows are concentrated, for instance at entrances to bays and rivers or between land masses where water currents are concentrated.

However, it is not always possible to arrange the power stations in such high velocity areas. For instance, locally the water may be shallow so that the presence of power stations at the bottom of the water volume may impede shipping traffic. Another drawback is that the application of these known hydroelectric power stations is restricted to these high velocity areas, which may be far away from the locations where the electrical power is actually needed. Furthermore, constructing the power stations in high- velocity areas may prove difficult in view of the environmental conditions. Consequently, there is a demand for hydroelectric power stations that can be applied also outside the high velocity areas mentioned above. Furthermore, power stations presently in operation are able to generate electrical power

Document GB 2 434 407 A discloses a tidal wave power generator comprising a vertical axis turbine and flow guides shaped to ensure that the water rotates the turbine in one direction. The flow guides are formed by a number of side walls, upper walls and lower walls, which walls together form a plurality of funnels that are able to increase the pressure effecting the turbine. Both the turbine and the walls have been put on a solid concrete base in a frustum pyramid shape. The assembly of concrete base, turbine and walls is sunk under water. Since the assembly is formed as one unit, the handling thereof may be problematic in case the generator is to generate a high power. Consequently, by arranging the walls and turbine on a single base, the maximum size of the assembly and thereby the maximum power to be generated by the assembly is restricted. Furthermore, the angle between the flow guides of the tidal wave power generator disclosed in GB 2 434 407 A is large and this causes enormous turbulence so this power generator will have a very low efficiency.

It is an object of the present invention to provide an improved flow operated power generating system for generating electrical power and/or an improved method of constructing the same. It is further object of the present invention to provide a power generating system that is capable of converting the kinetic energy of a fluid flow into electrical power in a more energy efficient way.

It is still a further object of the present invention to provide a tidal flow operated power generating system that is capable of generating more power than the prior systems.

At least one of the objects is achieved according to a first aspect of the present invention in a fluid flow operated power generating system for generating electrical power comprising:

- a turbine support arranged or configured to be arranged at a foundation at the bottom of a volume of water, in particular a sea or river;

- a turbine mounted to the turbine support and comprising an essentially vertical rotor having a plurality of vanes; - a plurality of fluid guiding elements arranged or to be arranged at a foundation at the bottom of the volume of water, the guiding elements being configured to increase the generated power through increasing the flow velocity of the fluid passing the turbine and extending generally radially with respect to the turbine. By increasing the flow velocity in an effective manner the generated power can be increased equal to the cubed flow velocity.

The turbine support and the guiding elements may be arranged separately on one or more foundations at the bottom of the volume of water and hence the scale of the power generating system may be made much larger than the scale of the usual power generator stations. This makes it possible, for instance, to substantially increase the power that can be generated by the system. Since the guiding elements extend generally radially with respect to the turbine, the fluid is concentrated in the centre where the turbine may be arranged in order to give the fluid passing the turbine (and thereby driving it) a relatively high velocity. In a further embodiment the guiding elements should therefore be arranged in a star-like configuration and the turbine should be arranged centrally in this configuration.

In embodiments of the invention the guiding elements are generally straight. Furthermore, the angle between neighbouring guiding elements should be an acute angle in order to reduce turbulence. More specifically, the angle defined between neighbouring guiding elements is preferably smaller than 60 degrees, even more preferably smaller than 45 degrees or smaller than 30 degrees, to further reduce turbulence. Turbulence may cause the power generating efficiency of the turbine to drop considerably.

In other embodiments of the present invention a guiding element comprises a generally straight first guiding element part and a generally curved second guiding element part, the second guiding element part being situated close to the position of the turbine and being arranged to further increase the velocity of the fluid passing the turbine. This has a positive influence on the maximum power generated by the generator. Similarly to the embodiment wherein the guiding elements is straight along its entire length, the angle defined between neighbouring guiding elements should be an acute angle or, more preferably, smaller than 60, 45 or 30 degrees, with a view to reduce turbulence. In an embodiment of the invention the guiding elements form one or more funnels to increase the flow velocity of the fluid passing the turbine. In an especially advantageous embodiment the guiding elements are formed by elongated dams constructed on top of the foundation at the bottom of the volume of water. In an embodiment of the present invention the effective ratio of the length

(L) of each of the guiding elements relative to the diameter (D) of the turbine is in a range of about 1 to about Vh ₂ Zv ₁ ,max, wherein h is the depth of the volume of water and v is the original velocity of the fluid, i.e. the velocity without the presence of the guiding elements. If the length of the guiding elements increases, the damming up of the water (i.e. the local rise of the water level) caused by the presence of the guiding elements and the turbine is increased as well. The damming up of the water puts a limit to the efficiency of the system. The diameter of the turbine needs therefore to be increased as well to avoid the situation wherein the ratio exceeds Vh ₂ Zv ₁ ,max. This avoids extensive raise of the water level and any counter-currents and side-currents to occur. In an embodiment the height of the guiding elements is larger than the local depth of the volume of water added with the local raise of the water level due to the presence of the guiding elements. In this way the top of the guiding elements is always above the water level.

The portion of the guiding element facing the turbine may extend generally in line with or parallel with the tangent of the outer portion of each of the vanes of the turbine so that a relatively smooth transition between the guiding element and a vane can be accomplished. This has a positive effect on the efficiency of the system.

In a preferred embodiment the number of guiding elements is eight and the angle between consecutive guiding elements is about 45 degrees, depending on the flow velocity pattern two or more sidewalls can be left away.

In an embodiment the angle between consecutive guiding elements is essentially constant. Since in this embodiment the guiding elements are evenly distributed around the turbine, the power generation may be performed substantially independent of the (tidal) flow direction. In an embodiment a guiding element is comprised of a plurality of prefabricated guiding sub-elements to be arranged in an abutting manner on the foundation. For instance, the sub-elements may be formed of caissons configured to float on the volume of water in a first mode of operation and to be sunk to the bottom of the volume of water in a second mode of operation. In this way the guiding elements may be constructed and arranged at the bottom in a cost-effective, fast and reliable manner.

According to another aspect of the invention on or more objects are achieved in a method of constructing a fluid flow operated power generating system, the method comprising:

- arranging a turbine support on a foundation at the bottom of a volume of water, in particular a sea or river;

- mounting a turbine to the turbine support, the turbine comprising a rotor having a plurality of vanes, the rotor extending generally vertically;

- arranging a plurality of fluid guiding elements on a foundation at the bottom of the volume of water, the guiding elements being arranged in a pattern configured to increase the flow velocity of the fluid passing the turbine.

Further advantages, characteristics and details of the present invention will become apparent when reading the following description of several embodiments thereof. In the description reference is made to the annexed drawings, in which show:

Figure 1 a schematic top view of an embodiment of the invention, applied in a river;

Figure 2 a schematic top view of a second embodiment of the invention, arranged at the bottom of the sea;

Figure 3 a schematic top view of a third embodiment of the invention; Figure 4 a side view in perspective of an embodiment of a turbine according to an embodiment of the invention.

In figure 1 a first embodiment of a fluid operated power generating system 1 according to the invention is illustrated. Figure 1 shows a river (R) in the middle of which a power generating system 1 is arranged. The direction of the water current in the river is denoted by Pi. On foundations 10-10'" on the river bed a plurality of guiding elements 2,3,5,6,9,14 in the shape of dams are arranged. The first, second and third dam 2,3 and 9 are arranged upstream of the central turbine 7, while the fourth, fifth and sixth dams 5, 6,14 are arranged downstream of the turbine 7. The guiding elements 2,3,5,6 are shown to have generally straight shape, but other shapes are possible as well. The upstream guiding elements 2,3,9 define a first set of funnels 11 in which the water streaming down the river can be received. Similarly, the downstream guiding elements 5, 6,14 define a second set of funnels 12 at the downstream end of the system 1 for discharging the water that has passed the turbine 7.

The guiding elements are arranged so that the angle (αi) between the first and second guiding element 2,3, the angle (α ₂ ) between the second and third guiding element 3,9, the angle ((X ₃ ) between the fourth and fifth guiding element 5,6 and/or the angle the angle (α ₄ ) between the fifth and sixth guiding element 6,14 is smaller than 60 degrees in order to reduce turbulence of the water flowing along the guiding elements. In the shown embodiments the angles (Xi ₁ (X ₂ , (X3, and α ₄ are substantially equal (about 30 degrees). In other embodiments one or more of the angles may take a different value. The specific arrangement of the guiding elements causes the velocity (v ₂ ) at the exit of the funnel 11 to be considerably larger than the velocity (V ₁ ) at the entrance thereof. This has a positive effect on the maximum power that can be generated by the turbine 7.

The amount of fluid entering the entrance of the funnel 11 formed by guiding elements 2,3 depends on the angle α between the dams. When the angle α is large, for instance between 60 and 90 degrees, no substantial increase of the velocity of the flow may be accomplished. However, when the angle α between the guiding elements is smaller than 60 degrees, or, preferably, smaller than 45 degrees, the turbulence will be reduced and the velocity increase may be substantial. When the angle between the guiding elements is as small as about 30 degrees, practically no turbulence will occur.

As mentioned earlier, in the centre between the upstream guiding elements 2,3 and the downstream elements 5, 6 a turbine 7 is positioned. The turbine 7 is mounted to a turbine support 8 that is configured to be arranged on a foundation 13 and/or supported on the guiding element (cf. broken lines) present on the river bed.

Referring to figure 4, the turbine 7 comprises a vertical rotor 16 preferably a cylindrical rotor, provided with a number of curved vanes. The rotor 16 is coupled to a generator (shown schematically in figure 4) that is capable of converting mechanical energy (rotation of the rotor 16) into electrical energy. The generated electrical energy is transported to a distribution station 26 for distribution to the end users. The velocity (V ₂ ) at the exit of the upstream funnel 11 can be calculated as being the velocity (V ₁ ) at the entrance of the funnel times the ratio of the flow area (Ai) at the entrance of the funnel and the flow area A ₂ at the exit of the funnel, minus losses by turbulence, counter currents and side currents . Furthermore, the power that can be generated with a turbine in this configuration may be approximated as P= l/2ηpAv ³ , wherein η is the efficiency of the turbine, p is the density of the fluid (i.e. the density of water), A is the effective rotor surface of the turbine and v is the velocity of the fluid passing the turbine. Suppose the rotor surface is 100 m ² , the angle α between the first and second guiding elements is 45 degrees, the flow velocity is 0,45 m/s after losses by counter currents and side currents , the area at the exit of the funnel 11 is 50 m ² and the efficiency is about 70%, then the power generating system is capable of generating about 70 MW.

When the river is in fact an estuary, the direction of the flow in the river or sea may be reversed as result of tidal changes. When the direction is reversed, the fourth, fifth and sixth elements 5, 6, 14 will perform a similar function as the first, second and third guiding elements 3, 4, 9 in the situation described above. The fourth, fifth and sixth guiding elements 5, 6, 14 cause an increase of the velocity of the flow passing the turbine, thereby increasing the maximum electrical power that can be generated. In situations where no reversal of the flow takes place, the opposite guiding elements may be dispensed with. In situations where no side flow takes place, the side guiding elements may be dispensed with.

Figure 2 shows another embodiment of the present invention. In this embodiment the power generating system is arranged at the bottom of the sea. The turbine 7 is mounted to support 8 and support 8 is arranged on the foundation 13 provided at the bottom of the sea. Centred around the turbine a plurality of elongated dams 18 extend in a generally radial direction. The elongated dams 18 are placed on individual foundations 10 (not shown in figure 2). Dams 18 extend from the sea bottom to a height slightly above sea level, i.e. a height larger than the local depth of the sea added with a predetermined amount of extra height due to the fact that the water level may be raised locally because of the presence of the dams. In the shown embodiment eight dams 18 have been arranged at the sea bed which dams have been evenly distributed in a star- like configuration around the central turbine. The angle α between neighbouring dams 18 therefore is about 45 degrees. The number of dams 18 may be chosen to be smaller or larger, depending on the circumstances.

Similar to the embodiment described in connection with Figure 1, the arrangement of the dams 18 is such that the velocity of the flow at the location of the turbine is much larger than the velocity at the entrance of the funnels formed by the dams 18. However, due to the specific configuration, the increase of the flow velocity is essentially independent of the direction of the flow. Whereas the first embodiment is configured to cope with a stream flowing in one or two (opposite) directions, the present embodiment is therefore able to generate power substantially independently of the direction of the tidal current.

Figure 3 shows a further embodiment of the present invention, based on the second embodiment described in connection with Figure 2. In the third embodiment the generally straight dams 18 have been given a curved part 19 close to the turbine. The curved parts of the dams have been provided to locally change the direction of the flow so that it better is adapted to the shape of the vanes of the turbine. This has a positive effect on the efficiency (i.e. on the efficiency coefficient η) of the turbine. The inventors found that preferably the effective ratio of the length (L) of each of the guiding elements relative to the diameter (D) of the turbine should be in a range of 1 to about Vh ₂ ZVi _max , wherein h is the depth of the volume of water and v is the original velocity of the fluid. In most situations in practice the effective ratio thus defined should be lower than about 8. The exact value of the ratio depends amongst others on the depth of the volume of water and the predominant average velocity of the tidal flow. For instance, in very deep water (depth more than 40 meters) and a relatively low velocity, the ratio should be about 8. The ratio may have to be reduced when the velocity of the flow is larger. In Table 1 below an overview is given of some preferred ratios of the length of the dam relative to the diameter of the turbine for several sea conditions and for several sea depths. Table 1 Overview of effective ratio 's as function of velocity and depth

The guiding elements or, more specifically, the dams, may be constructed in various ways. For instance, the material of the elements such as steel or concrete may be deposited on the (foundations at the) bottom of the sea, for instance by making use of a suitable hoisting equipment. In another example the guiding elements are formed by a number of sub-elements that can be arranged one behind the other at the bottom of the sea. In a particular advantageous embodiment the sub-elements are prefabricated (concrete) elements. The elements are fabricated on land. Since in a first mode of operation the elements can float on the water, they are towed to the location at sea (or at the river) where the power generating system is to be arranged. Then, in a second mode of operation, the elements are caused to sink and are placed one behind the other at the bottom. A combination of both examples is possible as well. For instance the floatable sub-elements may be arranged at the (foundation provided on the) sea bed, after which they are filled with material. For smaller configurations the total construction consisting out of a foundation inclusive walls can be fabricated on land and sunk at the bottom of the sea (or at the bottom of the river) In general, the height of the dams is such that the top of the dams always extends above the maximum level of the water so as to avoid any unwanted flows of water due to the pressure differences caused by the presence of the dams.

In particularly preferred embodiments the length of each of the guiding elements is between 5 and 55 m for shallow water with the depth of about 7 m or less, between about 15 m and 80 m for medium shallow water with a depth of about 7-15 m, between about 40 m and 220 m for deep water with a depth of about 15-30 m and/or about between 120 m and 620 m for very deep water with a depth of 30 m or more.

Although the invention has been described with reference to specific embodiments thereof, it will be appreciated that the invention is not limited to these embodiments and changes and modifications to the power generating system and the method described therein may be made without departing from the scope of the invention. The rights applied for are defined by the following claims.